1. Field of the Invention
The present invention relates to a photomultiplier for multiplying photoelectrons emitted in response to incident light which has reached a photocathode and, in particular, to a photomultiplier having a structure for making the area of an effective light entrance region for the incident light become greater than the area of the light receiving surface of the photomultiplier.
2. Related Background Art
Conventionally, as an optical sensor for measuring weak light or the like, so-called head-on type photomultiplier has widely been used. In the head-on type photomultiplier, one end of a cylindrical vacuum container constitutes a faceplate. Though the vacuum container of such a head-on type photomultiplier is made of a glass tube in general, there has recently been developed, as disclosed in Japanese Patent Application Laid-Open No. 6-310084 or the like, a photomultiplier constituted by a cylindrical metal tube and a faceplate (where a photocathode is disposed) disposed at one end thereof and supported by a flange extending toward the tube axis of the metal tube.